A universal fast and easy access at room temperature to transparent sols of nanoscopic Eu and Tb doped CaF, SrF and BaF particles via the fluorolytic sol-gel synthesis route is presented. Monodisperse quasi-spherical nanoparticles with sizes of 3-20 nm are obtained with up to 40% rare earth doping showing red or green luminescence. In the beginning luminescence quenching effects are only observed for the highest content, which demonstrates the unique and outstanding properties of these materials. From CaF:Eu10 via SrF:Eu10 to BaF:Eu10 a steady increase of the luminescence intensity and lifetime occurs by a factor of ≈2; the photoluminescence quantum yield increases by 29 to 35% due to the lower phonon energy of the matrix. The fast formation process of the particles within fractions of seconds is clearly visualized by exploiting appropriate luminescence processes during the synthesis. Multiply doped particles are also available by this method. Fine tuning of the luminescence properties is achieved by variation of the Ca-to-Sr ratio. Co-doping with Ce and Tb results in a huge increase (>50 times) of the green luminescence intensity due to energy transfer Ce → Tb. In this case, the luminescence intensity is higher for CaF than for SrF, due to a lower spatial distance of the rare earth ions.

Vitrimers are a class of polymeric materials with outstanding properties. Intramolecular substitution reactions lead to a dynamic exchange within the polymer network which enables thermoreversible stress relaxation in yet permanently crosslinked materials. In this paper, the acid‐mediated autocatalysis is explored as a rearrangement pathway for vinylogous urethane vitrimers. The autocatalysis enables transimination reactions, resulting in a dynamic exchange among the enamine‐one species, without an excess of free amines. Therefore, the enamine‐ones are protonated by a Brønsted acid and turn into electrophilic iminium‐ones, thus enabling fast backward and substitution reactions with water and free amines. This work provides an in‐depth investigation of the mechanism by kinetic studies of selected compounds. In addition, novel elastomeric and thermosetting poly(vinylogous urethane) networks with and without free amine groups and additional para‐toluene sulfonic acid as a Brønsted catalyst are prepared by bulk polymerization of hexane‐1,6‐diylbis(3‐oxobutanoate) and tris(2‐aminoethyl)amine. The underlying exchange mechanisms are determined by stress‐relaxation experiments with stress relaxation times of 0.3–54 000 s at 110 °C.

An efficient, fast and easy construction kit using the fluorolytic sol–gel synthesis of rare-earth-doped alkaline earth fluoride core–shell nanoparticles at room temperature is presented, capable of synthesizing several hundred grams to kilograms of core–shell particles in one batch.

Vitrimers belong to the class of covalent adaptable networks and are cross-linked polymers, which undergo dynamic, associative exchange reactions under thermal treatment, making these networks permanent as well as dynamic....

Vitrimers represent permanent and dynamic polymer networks at the same time. The combination of dynamic covalent bonds and widely available, biodegradable, and biobased raw materials enables new polymers with an excellent carbon footprint, mechanical properties, and outstanding features in terms of multiple recycling methods, e.g., thermomechanical, chemical, and biological reprocessing/reusability. Natural corn starch granules have been surface-modified by an acetoacetylation reaction without using any additional solvent and maintaining the inner semicrystalline structure, giving a polyfunctional cross-linker for starch-reinforced vitrimer composites. Vinylogous urethane vitrimer matrices were synthesized by the condensation reaction of fully acetoacetylated glycerol and different diamines, while glycerol and the diamines were deliberately selected as potentially biobased raw materials. Seven different matrix vitrimers were synthesized with a content of 0–70 wt % of modified starch and investigated in terms of their thermal and mechanical properties. In total, 20 elastomeric and thermosetting materials have been prepared, exhibiting high elastic moduli of 2 GPa with short stress relaxation times and a high content of modified starch up to 70 wt %. The composites show low swelling ratios, suppressing the natural gelatinization of starch in water. Moreover, suitable thermomechanical, chemical, and enzymatic recycling methods for closed-loop cycles, remolding, reusability, and biodegradability were developed.